Traditional cell-based processes for amplification of DNA in large quantities are costly. For example, use of bacteria requires their growth in large volumes in expensive fermenters that are required to be maintained in a sterile state in order to prevent contamination of the culture. The bacteria also need to be lysed to release the amplified DNA and the DNA needs to be cleaned and purified from other bacterial components. In particular, where DNA vaccines or other therapeutic DNA agents are produced, high purity is required to eliminate the presence of endotoxins which are toxic to mammals.
In addition to the issues of cost, use of bacteria can in many cases present difficulties for fidelity of the amplification process. In the complex biochemical environment of the bacterial cell, it is difficult to control the quality and yields of the desired DNA product. The bacteria may occasionally alter the required gene cloned within the amplified DNA and render it useless for the required purpose. Recombination events may also lead to problems in faithful production of a DNA of interest. Cell-free enzymatic processes for amplification of DNA avoid the requirement for use of a host cell, and so are advantageous.
For example, the manufacture of medicinal DNA cassettes relies almost exclusively on their insertion into bacterial plasmids and their amplification in bacterial fermentation processes.
This current state of the art process limits opportunities for improving the manufacture of such DNA medicines in a number of ways. In addition, the plasmid product is essentially a crude DNA molecule in that it contains nucleotide sequences not required for its medicinal function. Accordingly, in the field of production of DNA products, such as DNA medicines, there is a need to provide improved methods for amplification of DNA in large quantities. In particular, there is a need to provide improved methods for amplification of specific forms of DNA, such as closed linear DNAs. Closed linear DNA molecules have particular utility for therapeutic applications, as they have improved stability and safety over other forms of DNA.